These known compounds are used in numerous fields, in particular in medicine as radiopaque substances (X-ray contrast agents) or as oxygen transporters in blood substitutes. A compound which has been especially studied in this field is n-perfluorooctyl bromide, C.sub.8 F.sub.17 Br.
The following may be pointed out more particularly among the known methods for the preparation of these compounds:
the reaction of bromine wtth a compound R.sub.4 -SF.sub.5 at 500.degree. C. in the presence of nickel (U.S. Pat. No. 3,456,024), PA1 the gas-phase photolysis of a mixture of a 1-hydrogenperfluoroalkane and BrCl or BrF (Adcock et al, Chem. Abstr. 100: 34092 e), PA1 the reaction of bromine with the compounds R.sub.f -I in the presence of a free-radical intiator such as AIBN (Japanese Application Kokai 85-184033), and PA1 the photobromination of these same iodine compounds by UV irradiation (Huang et al, Huaxue Xuebao, 42(10) 1106-8 (1984), abstracted in Chem Abstr. 102: 78312 x). The preceding references are hereby incorporated by reference. PA1 fast kinetics, hence a high productivity capable of reaching about 0.5 mol/hour/liter of reactor, and PA1 operational reliability: simultaneous and controlled removal of hydrochloric acid and sulphur dioxide.
The low yields obtained and/or the slow kinetics of these methods are such that they do not permit economic production of perfluoroalkyl bromides on an industrial scale. In view of the importance of these compounds in the medical field, it is of great interest to be able to manufacture them at the lowest possible cost.